ISLAMABAD - An American missile attack killed 12 militants on the Pakistani side of the Afghan border on Friday, one of only a handful of such strikes this year, Pakistani officials said.

The missile struck in the Mandao district of South Waziristan, a rugged militant stronghold where the Pakistani army has staged offensives in the past, the officials said, giving no further details. The officials did not give their names because they were not authorized to speak to journalists.

It took place hours after al-Qaida confirmed that a strike last month in North Waziristan killed one of its commanders -- a success in a CIA-led campaign, but a major source of tension plaguing the relationship between Washington and Islamabad.

The strikes, which began in earnest in 2008, have killed scores of militants, including foreign al-Qaida members involved in plotting attacks on the West. Their frequency increased in 2010, when they hit militants widely seen as being proxies of the Pakistani army, causing friction between the U.S and Pakistan.

Reflecting the tensions, the number of attacks dropped in 2011, and they were cut back even more after November, when U.S. aircraft mistakenly killed 24 Pakistani troops on the Afghan border. Pakistan blocked U.S. supply routes into Afghanistan in protest and said it was renegotiating its ties with Washington as a result.

Friday's attack was the eight this year. In contast, in 2010, there were more than 150 such strikes.

Faced with strong public anger over the drone attacks, Pakistani officials publicly condemn them as an unacceptable violations of sovereignty that boost support for extremism. Privately, the program has long had some level of official sanction and even co-operation.

The confirmation of the death of militant commander Badr Mansoor is significant, because he was believed to be behind many of the suicide attacks that have killed scores of Pakistani civilians in recent years. It could be used by supporters of the campaign in Washington and Islamabad as an example of how drone attacks benefit both countries.

The U.S.-based SITE monitoring service said on Friday that the confirmation of Mansoor's death came in a video statement by Ahmad Farooq, al-Qaida's head of media and preaching in Pakistan. The video was released on an Internet jihadist forum.

Local Taliban fighters previously said Mansoor was killed in the Feb. 9 strike, but there was no confirmation from the U.S. or Pakistan. A militant video eulogizing the dead is considered the most reliable way of knowing when a top commander has been killed.

In the nine-minute video, which featured photos of Mansoor alive and dead, Farooq accused Pakistan of collaborating with the strikes.

"America is now more eagerly attacking the Pakistani government's targets," he said. "The drone program is being run with the full consent, permission and co-operation of the Pakistani government."

The issue of drone strikes -- their frequency, targeting and whether Pakistan should be informed ahead of them -- is key to ongoing, back-channel negotiations to restart U.S.-Pakistani relations, which are important for America's hopes of withdrawing from Afghanistan.

Mansoor was said to have run a militant camp in North Waziristan region, an al-Qaida and Taliban stronghold where the Pakistani army doesn't launch offensive operations, giving the militants a safe haven -- aside from the drone strikes.

Mansoor was from Pakistan's largest province, Punjab, and moved to North Waziristan in 2008, where he led a faction of some 230 fighters, local insurgents have said. The enlistment of Punjabis in the Pakistani Taliban has been a serious concern for the government, because it makes it easier for the militants to export violence from the border to the heart of the country, where most Punjabis live.